The present invention relates to the use of a component of a polymerisable liquid crystalline mixture in the production of orientated liquid crystalline polymers; compounds used as components in polymerisable liquid crystalline mixtures; liquid crystalline mixtures comprising these components, liquid crystalline polymers prepared from such components and liquid crystalline devices comprising those compounds.
Liquid crystal polymers (LCPs) are used in the manufacture of optical components such as waveguides, optical gratings, filters, retarders, piezoelectric cells and non-linear optical cells and films. The choice of LCP for use in any one of the aforementioned optical components depends upon its associated optical properties such as the optical anisotropy, refractive index, transparency and dispersion. Optical filters, for example, contain LCPs having a large anisotropy (xcex94n) and a low dispersion (n=f(xcex)).
In some applications there is a requirement to produce LCPs in which the component molecules adopt a specific tilt angle with respect to the plane of the substrate. These LCP materials can be used as optical components such as compensation layers and retarders. Such optical components may be used in the production of liquid crystal devices (LCDs) with improved viewing angles, for example.
LCPs are manufactured by orientating a layer of a polymerisable liquid crystal single compound or mixture on an orientated substrate and cross-linking the mesogenic layer to form a liquid crystal polymer (LCP) network. Polymerisable LC compounds used in the manufacture of the LCPs need to be chemically and thermally stable, stable to electromagnetic radiation, soluble in standard solvents, miscible with other LC components and exhibit liquid crystalline properties over the range 25 to 150xc2x0 C., preferably 25 to 80xc2x0 C. The configuration imposed by the orientation layer on the polymerisable LC single compound or mixture becomes fixed or frozen into the LCP network formed upon cross-linking. The resulting LCP films have a high viscosity and are stable to mechanical stresses, temperature and light exposure.
The tilt angle adopted by the polymerisable LC single compound or mixture prior to cross-linking depends in part upon the nature of the LC components comprising that single compound or mixture. Previous strategies employed in generating a tilt angle in a given LC single compound or mixture prior to cross-linking have, for example, relied upon the introduction of one or more lateral substituents into the meosogen, such as a short aliphatic alkyl chain. However, such substitution is accompanied by a decrease in the mechanical properties of the LC material or, depending upon the molecular architecture of the mesogen, is associated with a small or vanishing tilt angle. In each case the reproducibility of the initial tilt is readily lost before the mixture is cross-linked to give the LCP network due to thermal and mechanical effects.
There is therefore a need for a liquid crystalline single compound or mixture that can be orientated on a substrate prior to cross-linking in such a way that the orientation of the LC single compound or mixture on the substrate remains stable over the period required for manufacturing the LCP network. There is also a need for a LC component with the ability to facilitate the generation of and maintain a wide range of predetermined tilt angles prior to and during the manufacture of the LCP film. The present invention addresses those needs.
A first aspect of the present invention provides the use of a component of a LC mixture in the manufacture of a LCP network comprising the mixture, characterised in that the component induces a stable tilt angle in the LCP network. By the word stable it is to be understood to mean that there is no substantial change in the value of the tilt angle over the period necessary for manufacturing the LCP network. The LCP network obtained by cross-linking the polymerisable LC mixture can be a nematic, smectic A or discotic film, but is preferably a nematic film. These films are characterised by good orientation of the film components relative to the substrate.
The component used to induce a stable tilt angle is preferably mesogenic in nature or is compatible with a mesogenic molecular architecture and may contain polymerisable or non-polymerisable substituents. It is preferably miscible with the other components of the liquid crystal mixture. Without wishing to limit the scope of the invention, it is believed that the component must contain a sterically bulky group that has the ability to form a strong association with the substrate or with the orientation layer. The component should also contain a sterically less bulky group that is compatible with a mesogenic molecular architecture and which extends into the bulk of the LC single compound or mixture as a whole. It is believed that this mesogenically compatible group is able to assume an angle in which it is tilted relative to the plane of the substrate. Unlike the LCP mixtures of the prior art, LCPs including these components are less susceptible to thermal effects and the polymerisable LC single compound or mixture comprising or including a component of the present invention is able to retain its initial orientation over the period necessary for manufacturing the LCP network. Judicious choice of the substrate associating and mesogenic extending groups allows this angle to be varied. It will be appreciated that the components of the invention can therefore be used in the manufacture of polymerisable LC single compounds or mixtures having a stable orientation or tilt angle relative to the plane of the substrate.
By sterically bulky it is to be understood that the lateral dimensions of the substrate associating group are at least half as large again as the lateral dimensions of the less bulky group, preferably two or more times the dimensions of the less bulky group.
The substrate associating or more bulky groups preferably comprise organosiloxane groups and the mesogenic extending or less bulky groups preferably contain aromatic or non-aromatic carbocyclic or heterocyclic ring systems. It is believed that the organosiloxane containing components used in the first aspect of the invention include compounds that are new per se and a second aspect of the invention provides an organosiloxane compound of formula I 
wherein
B1 to B4 each individually represent a spacer group selected from the group comprising optionally substituted saturated or unsaturated, straight chain or branched chain C1-80 alkyl group, one or more of the non-adjacent alkyl CH2 groups being optionally replaced by one or more heteroatoms;
B5 represents a hydrogen atom or spacer group as defined above,
A1 and A2 each individually represent a single bond or a spacer group as defined above,
MG1 to MG3 each individually represent a mesogenic group comprising at least one optionally substituted aromatic or non aromatic carbocyclic or heterocyclic ring systems; and
n1 and n2 are each independently 0 or a positive integer with the proviso that, firstly, when n2 is 0 both B1 and B2 include a polymerisable group and at least one of A1, B1 and B2 includes a group selected from an organosiloxane, an organogermanium, an organotin and an organo-perfluoro residue and secondly, when n2  greater than 0 at least one of B1, B2, B3 and B4 includes a polymerisable group and at least one of A1, A2, B1, B2, B3 and B4 includes an organosiloxane group.
By the term xe2x80x98heteroatomxe2x80x99 it should be understood to include nitrogen, oxygen and sulphur. Replacement nitrogen atoms may be further substituted with groups such as alkyl, aryl and cycloalkyl. These compounds have been found to be particularly useful in the preparation of liquid crystalline polymer networks (LCPs) in which the molecules are tilted with respect to the orientation layer. These LCPs can be used in a range of different optical and electrical applications. LCP networks having nematic, smectic A and surprisingly discotic properties may be prepared. Nematic mesophases are preferred.
Most of the discotic liquid crystalline compounds described in prior art are based on disc-shaped molecules (such as triphenylene) which are characterised by a rigid and highly conjugated aromatic central core. These discotic compounds are of limited use because of properties such as a high viscosity, a high melting point, near visible light absorption and problems in their preparation, which also hinders the chemical diversity of the compounds that may be prepared.
There is, therefore, a need for new discotic liquid crystalline materials having reduced melting points and viscosities compared to those obtained with calamitic liquid crystals.
The present inventors have surprisingly found that discotic mesophases may be obtained from rod-shaped molecules, which are more easily prepared and offer the possibility of preparing material having diverse molecular structures. These discotic mesophases may be obtained from molecules having calamitic architecture, by introducing into each one of their peripheral alkyl chains, at least one bulky group which is not compatible (in the liquid crystalline state), with the other molecular constituents. This non compatibility means that these bulky groups tend to associate in the mesophase leading to separate micro layers.
The presence of the bulky groups in each of the peripheral alkyl chains causes the central rigid rod-shaped cores to adopt an intermolecular crossed configuration leading to disc-shaped elements which are able to form discotic mesophases.
The compound of formula (I) may be monomeric, oligomeric or polymeric in nature. It will be appreciated that the value of the integers n1 and n2 will be determined by the nature of the compound of formula (I). When the compound of formula (I) is monomeric or oligomeric in nature, n1 and n2 may assume values of from 0 to 10, preferably from 1 to 5. However when the compound of formula (I) is polymeric in nature the values of n1 and n2 can range from 6 to 3,000 preferably from 11 to 2,000.
The number of aromatic or non-aromatic ring systems present in the groups MG1 to MG3 will depend upon the application in which the compound of formula (I) is to be used. MG1 to MG3 preferably contain between 1 and 4 aromatic or non-aromatic ring systems.
The hydrocarbon spacer groups B1 to B4 may include C1-C20-alkyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, C1-C20-alkylcarbonyl and C1-C20-alkylcarbonyloxy groups, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, octyloxycarbonyl, nonyloxycarbonyl, decyloxycarbonyl, undecyloxycarbonyl, dodecyloxycarbonyl, methylcarbonyl, ethylcarbonyl, propylcarbonyl, butylcarbonyl, pentylcarbonyl, hexylcarbonyl, octylcarbonyl, nonylcarbonyl, decylcarbonyl, undecylcarbonyl, dodecylcarbonyl, methylcarbonyloxy, ethylcarbonyloxy, propylcarbonyloxy, butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, octylcarbonyloxy, nonylcarbonyloxy, decylcarbonyloxy, undecylcarbonyloxy, dodecylcarbonyloxy, and the like.
The optionally substituted C1-80 alkyl groups may be substituted by alkyl, aryl and cycloalkyl, as well as amino, cyano, epoxy, halogen, hydroxy, nitro, oxo etc. Possible heteroatoms, which may replace carbon atoms, include nitrogen, oxygen and sulfur. In the case of nitrogen further substitution is possible with groups such as alkyl, aryl and cycloalkyl. The optionally substituted aromatic or non-aromatic carbocyclic or heterocyclic ring systems may be similarly substituted.
Any one of the groups B1, B2, B3 and B4 may contain an organosiloxane group and a polymerisable group. Alternatively one or more of the groups B1, B2, B3, B4, A1 and A2 may contain an organosiloxane group with one or more of the other groups of B1, B2, B3 and B4 containing a polymerisable group. Preferably at least one of the groups B1 to B4 includes both a polymerisable group and an organosiloxane group and in a first preferred embodiment of the second aspect of the invention each or any of the groups B1 to B4 may be a hydrocarbon residue of formula (II)
Pxe2x80x94(Sp1)k1xe2x80x94[(Si(R1)2O)m1xe2x80x94Si(R2)2]m2xe2x80x94(Sp2)k2xe2x80x94(X1)t1xe2x80x94xe2x80x83xe2x80x83(II)
wherein
P is a polymerisable group selected from groups comprising CH2xe2x95x90CWxe2x80x94, CH2xe2x95x90Wxe2x80x94Oxe2x80x94, CH2xe2x95x90CWxe2x80x94COOxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94Phxe2x80x94, CH2xe2x95x90CWxe2x80x94COxe2x80x94NHxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(COORxe2x80x2)xe2x80x94CH2xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94Oxe2x80x94, CH2xe2x95x90CHxe2x80x94OOCxe2x80x94, Phxe2x80x94CHxe2x95x90CHxe2x80x94, CH3xe2x80x94Cxe2x95x90Nxe2x80x94(CH2)m3xe2x80x94, HOxe2x80x94, HSxe2x80x94, HOxe2x80x94(CH2)m3xe2x80x94, HSxe2x80x94(CH2)m3xe2x80x94, HO(CH2)m3COOxe2x80x94, HS(CH2)m3COOxe2x80x94, HWNxe2x80x94, HOC(O)xe2x80x94, CH2xe2x95x90CHxe2x80x94Phxe2x80x94(O)m4 
wherein
W represents H, F, Cl, Br or I or a C1-5 alkyl group;
m3 is an integer having a value of from 1 to 9;
m4 is an integer having a value of 0 or 1,
Rxe2x80x2 represents a C1-5 alkyl group;
Rxe2x80x3 represents a C1-5 alkyl group, methoxy, cyano, F, Cl, Br or I;
Sp1 and Sp2 each independently represent a C1-20 alkylene group;
k1 and k2 are integers, each independently having a value of from 0 to 4;
R1 and R2 each independently represent straight chain or branched C1-20 alkyl groups;
m1 is an integer having a value of from 0 to 10;
m2 is an integer having a value of from 1 to 10;
X1 represents xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94CH2 l xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond; and
t1 is an integer having a value of 0 or 1.
In relation to the hydrocarbon residue of formula (II), the term xe2x80x94Phxe2x80x94 is to be understood as representing 1,4-phenylene, 1,2-phenylene as well as 1,3-phenylene. 1,4-phenylene groups are preferred. The term Phxe2x80x94 or (Ph) should be understood to represent a phenyl group.
The C1-20 alkylene groups Sp1 and Sp2 may comprise branched or straight chain alkylene groups and may be unsubstituted, mono- or polysubstituted by F, Cl, Br, I or CN. Alternatively or in addition one or more of the CH2 groups present in the hydrocarbon chain may be replaced, independently, by one or more groups selected from xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NHxe2x80x94, N(CH3)xe2x80x94, xe2x80x94CH(OH)xe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94CH2(CO)xe2x80x94, xe2x80x94CH2(SO)xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94CH2(SO2)xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94OCOxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Sxe2x80x94, xe2x80x94SOOxe2x80x94, xe2x80x94OSOxe2x80x94, xe2x80x94SOSxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94(CF2)xe2x80x94r, xe2x80x94CD2)sxe2x80x94 or C(W1)xe2x95x90C(W2)xe2x80x94, with the proviso that no two oxygen atoms are directly linked to each other. W1 and W2 each represent, independently, H, Hxe2x80x94(CH2)q1xe2x80x94, F, Cl, Br or I. The integers r, s and ql each independently represent a number of between 1 and 15.
One or more of the CH2 groups of the C1-20 alkyl groups R1 and R2 may each be replaced, independently, by xe2x80x94Si(CH3)2xe2x80x94 or/and by xe2x80x94Si(CH3)2O Si(CH3)2xe2x80x94.
Compounds of formula (I) in which Aand/or A2 comprise an organosiloxane group are preferred and in a second preferred embodiment of the second aspect of the invention the groups A1 and/or A2 comprise a group of formula (III)
xe2x80x94(X2)t2xe2x80x94(Sp3)k3[(Si(R3)2O )m5xe2x80x94Si(R4)2]m6xe2x80x94(Sp4)k4xe2x80x94(X3)t3xe2x80x94xe2x80x83xe2x80x83(III)
wherein
Sp3 and Sp4 each independently represent the designations assigned to Sp1 and Sp2 above,
X2 and X3 each independently represent the designations assigned to X1 above,
R3 and R4 each independently represent the designations assigned to R1 and R2 above,
k3 and k4 are integers, each integer independently having a value of from 0 to 4,
t2 and t3 are integers, each independently having a value of 0 or 1; and
m5 is an integer having a value of from 0 to 10; and
m6 is an integer having a value of from 1 to 10.
The groups MG1 to MG3 may be the same or different and may comprise up to three bridging groups. A third embodiment of the second aspect of the invention provides compounds of formula (I) in which MG1 comprises a group of formula (IV)
xe2x80x94C1xe2x80x94(Z1xe2x80x94C2)a1xe2x80x94(Z2xe2x80x94C3)a2xe2x80x94(Z3xe2x80x94C4)a3xe2x80x94xe2x80x83xe2x80x83(IV),
wherein
C1 to C4 each independently represent a non aromatic, aromatic, carbocyclic or heterocyclic group;
Z1 to Z3 each independently represent xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94 or a single bond; and
a1, a2 and a3 are integers, each integer independently having a value of from 0 to 3, with the proviso that a1+a2 +a3 xe2x89xa63.
It is especially preferred that the groups C1 to C4 are selected from the following structural formulae: 
In a fourth embodiment of the second aspect of the invention the groups MG2 and MG3 comprise groups of formula (IVa)
xe2x80x94C5xe2x80x94(Z4xe2x80x94C6)a4xe2x80x94(Z5xe2x80x94C7)a5xe2x80x94(Z6xe2x80x94C8)a6xe2x80x94xe2x80x83xe2x80x83(IVa),
wherein:
C5, C6, C7 and C8 each independently represent a non-aromatic, aromatic, carbocyclic or heterocyclic group; and
Z4 to Z6 each independently represent xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94 or a single bond; and
a4, a5 and a6 are integers, each integer independently having a value of from 0 to 3,
with the proviso that firstly a4+a5+a6xe2x89xa63 and secondly that at least one of C5 to C8 independently comprises a trivalent group.
It is preferred that C7 is the trivalent group. It is especially preferred that C7 selected from one of the following structural formulae: 
wherein for each of the groups MG1 to MG3 of formulae (IV) and (IVa) respectively
L represents xe2x80x94CH3, xe2x80x94COCH3, xe2x80x94NO2, CN, or halogen;
u1 represents an integer having a value of from 0 to 4;
u2 represents an integer having a value of from 0 to 3; and
u3 represents an integer having a value of from 0 to 2.
In an especially preferred fifth embodiment of the second aspect of the invention there is provided a compound of formula (I)
wherein
n1 and n2 are independently 0 or 1;
B5 is hydrogen;
B1 to B4 each independently represent a group of formula (V)
P2xe2x80x94Sp5xe2x80x94[(Si(CH3)2O)m7xe2x80x94Si(CH3)2]m8xe2x80x94Sp6xe2x80x94X4xe2x80x94xe2x80x83xe2x80x83(V);
A1 and A2 each independently represent a group of formula (VI)
xe2x80x94X5xe2x80x94Sp7xe2x80x94[(Si(CH3)2O)m9xe2x80x94Si(CH3)2]m10xe2x80x94Sp8xe2x80x94X6xe2x80x94xe2x80x83xe2x80x83(VI)
wherein
X4 to X6 each independently represent xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, or a single bond, especially xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94 or single bond;
Sp5 to Sp8 each independently represent a C1-20 straight-chain alkylene group, especially ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, or dodecylene;
p2 represents CH2xe2x95x90CW5xe2x80x94 or CH2xe2x95x90CW5xe2x80x94(CO)v2Oxe2x80x94wherein
W5 represents H, CH3, F, Cl, Br or I; and
v2 is 0 or 1;
m7 and m9 are integers, each independently having a value of 1 or 2;
m8 and m10 are integers, each independently having a value of 0 or 1; with the proviso that m8+m10 greater than 0;
MG1 represents a group of formula IV wherein
C1, C2, C3 and C4 are the same and are selected from phenylene or biphenylene; and
Z1 to Z3 each independently represent a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94; and
MG2 and MG3 each independently represent a group of formula IVa wherein
C5, C6, and C8 are the same and are selected from phenylene or biphenylene;
C7 represents phenylene or biphenylene; and
Z4 to Z6 each independently represent a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94.
The surprising ability of the compounds of the invention to form discotic mesophases has been discussed to above. The compounds of the invention that have been found to be particularly suitable for the preparation of discotic mesophases are those having a bulky group in each of their peripheral alkyl chains B1 and B2. As mentioned previously it is believed that the presence of the bulky groups causes the rod-shaped molecules of the invention to associate thereby forming disc-shaped elements, which are stabilising to discotic mesophases.
Suitable bulky groups include fluorinated alkyl residues as well as and organic residues having bulky atoms such as germanium, silicon, and tin.
Preferably the bulky groups comprise organic residues having tetravalent bulky atom such as germanium, silicon, and tin. It is especially preferred that the bulky groups comprise at least one silioxane group. It is more especially preferred that each of the groups B1 and B2, include at least one siloxane group.
It is preferred that the central core of molecules having the ability to form a discotic mesophase comprises at least one optionally substituted aromatic or non-aromatic carbocyclic ring system. More preferably the central cores are selected from those that are able to induce a calamitic mesophase.
The bulky groups are preferably each independently attached to the central core of the molecule via a C1-20 alkyl spacer group as defined above.
A preferred sixth embodiment of the second aspect of the invention provides a compound of formula (I) in which
n1 and n2 are both 0,
B1 and B2 each independently represent a group of formula (VIl)
P3xe2x80x94Sp5xe2x80x94[Si(CH3)2O)m7xe2x80x94Si(CH3)2]m8xe2x80x94Sp6xe2x80x94X4xe2x80x94xe2x80x83xe2x80x83(VII);
wherein
X4 represents xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94,xe2x80x94COOxe2x80x94,xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond, especially xe2x80x94Oxe2x80x94,xe2x80x94COOxe2x80x94,xe2x80x94OCOxe2x80x94 or single bond;
Sp5 to Sp6 each independently represent a C1-20 straight-chain alkylene group, especially ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, or dodecylene;
P3 represents a hydrogen or CH2xe2x95x90CW5xe2x80x94 or CH2xe2x95x90CW5xe2x80x94(CO)v2Oxe2x80x94wherein
W5 represents H, CH3, F, Cl, Br or I; and
v2 is 0 or 1;
m7 is 1 or 2;
m8 is 1;
MG2 represents a group of formula IVa wherein
C5,C6, and C8 are the same and are selected from phenylene or biphenylene;
C7 represents phenylene or biphenylene; and
Z4 to Z6 each independently represent a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94.
These compounds are particularly suitable for the preparation of materials having discotic mesophases.
The compounds according to the second aspect of the invention may be readily prepared using methods that are well known to the person skilled in the art, such as those documented in Houben-Weyl, Methoden der Organischen Chemie, Thieme-Verlag, Stuttgart. In particular, the compounds may be readily prepared from direactive organosiloxane compounds according to any one of Schemes 1 to 5. A third aspect of the invention provides a method for the preparation of compounds according to the second aspect of the invention comprising reacting a direactive siloxane with a mesogenic compound comprising at least one carbocyclic or heterocyclic ring system. 
The organosiloxane compounds according to the second aspect of the invention may be used alone or as a component of a liquid crystal mixture. Liquid crystalline materials comprising a compound of formula (I) may be used in the manufacture of LCPs. A fourth aspect of the invention therefore comprises a liquid crystalline material comprising a compound of formula (I). Preferably the liquid crystalline materials comprises at least two components. The additional components must be miscible with the compound of formula (I) and may selected from known mesogenic materials such as those reported in Adv. Mater. 5, 107 (1993), Mol. Liq. Crsyt. 307, 111 (1997), J. Mat. Chem. 5, 2047 (1995) or in patent applications U.S. Pat. Nos. 5,593,617; 5,567,349; GB-A-2 297 556; GB-A-2 299 333; DE-A-195 04 224; EP-A-0 606 940; EP-A-0 643 121 and EP-A-0 606 939, optionally selected from EP-A-0 606 940; EP-A-0 643 121 and EP-A-0 606 939.
The form of the liquid crystal material will depend upon the application in which it is to be used and may be present as a liquid crystalline mixture, (co)polymer, elastomer, polymer gel or polymer network. Polymer networks have been found to be of particular use and in a first preferred embodiment of the fourth aspect of the invention there is provided a polymer network comprising a compound of formula (I) in cross-linked form. Preferably the polymer network comprises at least two components, at least one of which is an organosiloxane compound of formula (I).
The polymer network may be prepared by the copolymerisation of a mesogenic mixture comprising:
i) at least one chiral or/and achiral mesogenic polymerisable compound;
ii) at least one organosiloxane compound of formula I; and
iii) an initiator.
The chiral or achiral mesogenic polymerisable compound may be an organosiloxane compound of formula (I). Alternatively or in addition, the polymerisable compound may be selected from the known mesogenic materials referred to above. Preferably the chiral or achiral polymerisable compound includes the nematic phase in its thermotropic sequence.
The polymer network may optionally comprise further components. These include further polymerisable compounds, stabilisers and dyes. The additional polymerisable compounds preferably comprise a non-mesogenic compound having at least one polymerisable functional group, especially diacrylate compounds.
Any suitable stabiliser that prevents undesired spontaneous polymerisation, for example during storage of the mixture, may be used in the liquid crystalline mixture according to the invention. A broad range of these compounds is commercially available. Typical examples include 4-ethoxyphenol or 2,6-di-(t-butyl)-4-hydroxytoluene (BHT).
If colour filters are required, dyes may be added to the mixture. In a preferred embodiment of the invention the LC mixture contains no dye.
The chiral or achiral polymerisable mesogenic compound may be present in an amount comprising 0.01 to 99% by weight of the liquid crystalline polymer network mixture, preferably 50 to 95% by weight.
The organosiloxane compound of formula (I) may be present in an amount from 0.1 to 100% by weight of the liquid crystalline network, preferably from 1 to 50% by weight.
The initiator is preferably a photoinitiator and may be a radical or cationic initiator that is present in an amount comprising 0.1 to 5% by weight of the polymer mixture, preferably from 0.2 to 2% by weight.
When the mixture further comprises a stabiliser, this is generally present in an amount comprising 0 to 5% by weight of the liquid crystalline mixture, preferably from 0.1 to 1% by weight.
These polymerisable liquid crystalline mixtures may be formed into liquid crystalline polymer (LCP) films and a fifth aspect of the invention provides a LCP film comprising a compound of formula (I). LCP films may be readily prepared by UV polymerisation of a LC mixture according to the fourth aspect of the invention; a film comprising the LC mixture is formed on a substrate and polymerised using UV light to give a cross-linked liquid crystal polymer (LCP) film. The film is both light and temperature stable and can be used in the manufacture of devices such as waveguides, optical gratings, filters, retarders, piezoelectric cells or thin films exhibiting non-linear optical properties.
Different methods can be used for the formation of the sought LCP network, starting from the polymerisable liquid crystalline mixture manufactured as described above. Transparent substrates such as coated ITO (indium tin oxide), glass or plastic substrates, may be used. Preferred substrates include glass or plastic, especially those including a layer of rubbed polyimide or polyamide or a layer of photooriented photopolymer (LPP). Said layers are used to facilitate uniform orientation of the liquid crystalline mixture.
In the preparation of LCP films, it is particularly important to prevent the formation of defects or inhomogenities. This can be achieved by forming the polymerisable liquid crystalline mixture into a thin film; placing the mixture between two of the aforementioned substrates which are then sheared over a small distance until a planar order was obtained; or capillary filling the polymerisable liquid crystalline mixture between two of the said substrates prior to curing with, for example, by UV light, preferably in the presence of a photoinitiator, such as Irgacure(copyright).
The invention will now be described with reference to the following examples. Variations on these falling within the scope of the invention will be apparent to a person skilled in the art.
In the following Examples the thermotropic phases are abbreviated as follows: